Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$6.93	12.832%	$7.8193	$7.82	$7.80	$7.80
Purchase #2	$182.29	13.403%	$206.7223	$206.72	$206.70	$206.70
Purchase #3	$165.33	4.406%	$172.6144	$172.61	$172.60	$172.60
Purchase #4	$58.77	6.296%	$62.4702	$62.47	$62.45	$62.50
Purchase #5	$133.52	8.463%	$144.8198	$144.82	$144.80	$144.80
Purchase #6	$21.68	5.609%	$22.896	$22.90	$22.90	$22.90
Purchase #7	$14.50	6.500%	$15.4425	$15.44	$15.45	$15.40
7 purchase totals =	$583.02		$632.7845	$632.78	$632.70	$632.70